Coolant pump check

[Patrick Wong]

Originally Posted by bredekamp

Oh!?

but, but....why? Strict emissions laws?

California historically has had worse smog in major metropolitan areas (due to automobile pollution) vs. the other 49 states. For example, Los Angeles in the 60s was frequently covered by an ominous yellowish-grey smog blanket, and your eyes would hurt and water when exposed to the smog on the freeway. Therefore the US government allowed CA to establish tighter pollution regulations for automobiles.

Several years ago the California Air Resources Board required auto manufacturers to produce zero-emissions vehicles (ZEV). However, the deadline for ZEV vehicles was subsequently postponed as electric and hydrogen fuel cell vehicles were not deemed ready for prime time. As part of that postponement, the PZEV (partial zero-emissions vehicle) category was created.

Prius fits into an even more exclusive category of AT-PZEV (advanced technology PZEV). The coolant heat recovery system (CHRS) and the fuel tank bladder are part of the technology that qualifies Prius for that category. This also qualifies Prius for a longer hybrid system warranty in CA and other states that have adopted the CA standards (15 yr/150K miles).

Partial zero-emissions vehicle - Wikipedia, the free encyclopedia

The US Classic Prius did not have CHRS. Instead it had a fancy catalytic converter with a hydrocarbon absorption chamber (HCAC) that was supposed to temporarily hold excess HCs until the catalytic converter was hot enough to start working. However that system had a valve that was prone to failure. So when 2G was released, the HCAC system was discontinued in favor of CHRS.

Having owned both the 2001 (w/o CHRS) and the 2004 (w/ CHRS), I would not say that system noticeably improves mpg.